Security risk of server side text editing in general and vim.tiny specifically

[Fiedler Roman <Roman.Fiedler () ait ac at>]

Dear OSS-Security List,

Due to the recent discussion on vim swap file use, I expected also attraction of of evil-minded to the topic of text 
editing security and thus an increase in attack probability on server side text editing in general. Therefore I wanted 
to review our software qualification criteria for text editing on servers, where vim/vim.tiny is used and probably 
update the SOPs and guidelines.

As .swp security problems also arise from unclear software behaviour expectations, I looked at the behaviour of 
vim.tiny to verify it works according to specification (man pages as reference). As it seems, the tool is not suited 
for editing of files not owned by the same user, which is not mentioned in the man pages. Maybe that indicates, that 
the software design process did not include that specific security requirement or implementation was insufficient. 
Therefore I would assume, that numerous bugs of similar kind might be found, but there is no time (funding) to do in 
depth checks.

I would be interested in consensus, if editing of non-root files by root user is bad practice in general (thus, e.g. 
should be mentioned in SECURITY section of man pages of various common server side test editing tools to raise 
awareness, but no CVEs) or if you think, that this is software misbehaviour.

Input from "Solar Designer <solar at openwall x com>" to that topic:

"This discussion does not belong on the distros list.  Please bring it to
oss-security ASAP, including the PoC (or optionally delay it by at most
a week, but I see no reason for that as nothing will change in that week
anyway), and people will hopefully reply for real in there.

There's no embargoed issue here that I can see and no proposed unembargo
date either (a requirement for any initial posting to distros), I don't
see how anything will change within distros' list maximum embargo time
of 14 days, and it is indeed "bad practice in general" to access files
as root in user-writable directories, which is not at all limited to
text editors."


Best regards,
Roman Fiedler

PS: POC for vim.tiny on Ubuntu Xenial to overwrite arbitrary files as user root when editing file in directory owned by 
other user is available on request, disclosure after one week or if list discussion indicates other timing.

ROMAN FIEDLER
Scientist
Information Management
Center for Digital Safety & Security

AIT Austrian Institute of Technology GmbH
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